Zhilong Rao

High transmission through ridge nano-apertures on Vertical-Cavity Surface-Emitting Lasers.

We report high-intensity nano-aperture Vertical-Cavity Surface- Emitting Lasers (VCSELs) with sub-100nm near-field spots using ridge apertures. Power transmission efficiency through different ridge apertures, including bowtie, C, H and I-shaped apertures on VCSELs were studied. Significantly higher transmission efficiencies were obtained from the ridge apertures than those from conventional square apertures. Mechanisms for high transmission through the ridge apertures are explained through simulation and waveguide theory. A new quadruple-ridge aperture is proposed and designed via simulation. With the high-intensity and small spot size, VCSELs using these ridge nano-apertures are very promising means to realize applications such as ultrahigh-density near-field optical data storage and ultrahigh-resolution near-field imaging etc.

High-intensity bowtie-shaped nano-aperture vertical-cavity surface-emitting laser for near-field optics

We report a high-intensity nano-aperture vertical-cavity surface-emitting laser (VCSEL) utilizing a bowtie-shaped aperture. A maximum power of 188 microW is achieved from a 180 nm bowtie aperture at a wavelength of 970 nm. The near-field full width at half-maximum intensity spot size 20 nm away from the bowtie aperture is 64 nm x 66 nm from simulation, and the peak near-field intensity is estimated to be as high as 47 mW/microm(2). This intensity is high enough to realize near-field optical recording, and the small spot size corresponds to storage densities up to 150 Gbits/in(2). The bowtie-aperture VCSEL also enables other applications, such as compact high-intensity probes for ultrahigh-resolution near-field imaging and single molecule fluorescence and spectroscopy.

High-intensity C-shaped nanoaperture vertical-cavity surface-emitting laser with controlled polarization

The authors designed and demonstrated a C-shaped nanoaperture (C aperture) vertical-cavity surface-emitting laser (VCSEL) with a maximum far-field power of 157μW coming from a 70nm C aperture. Simulation shows that the near-field full width at half maximum spot size at 30nm away from the C aperture is 94×108nm2 in X and Y directions. The authors estimate the peak near-field intensity from the C-aperture VCSEL to be as high as 19mW∕μm2. This high intensity and small spot size are promising for realizing near-field applications such as near-field imaging and ultradense near-field optical data storage.

A C-shaped nanoaperture Vertical-Cavity Surface-Emitting Laser for high-density near-field optical data storage

We designed and demonstrated a unique C-shaped nanoaperture (C-aperture) Vertical-Cavity Surface-Emitting Laser with an estimated maximum net power of 113 μW coming from a 70nm C-aperture. Simulation shows the near-field FWHM spot size at 30nm away from the C-aperture is 94nm and 108nm in X and Y direction. We estimate the peak near-field intensity from the C-aperture VCSEL to be as high as 13.7mW/μm2. This high intensity and small spot size is promising to realize high-density near-field optical data storage.

Thick lattice-matched GaInNAs films in photodetector applications

The dilute-nitride GaInNAs shows great promise in becoming the next choice for long-wavelength (0.9 to 1.6 μm) photodetector applications due to the ability for it to be grown lattice-matched on GaAs substrates. GaAs-based devices have several advantages over InP-based devices, such as substrate cost, convenience of processing, and optoelectronic band parameters. This paper will present results from the first high-quality thick GaInNAs films grown by solid state molecular beam epitaxy with a nitrogen plasma source and the first high efficiency photodetectors which have been fabricated from those materials. GaInNAs films up to 2 microns thick have been grown coherently on GaAs substrates. These films exhibit reasonable photoluminescence intensities at peak wavelengths of 1.22 to 1.13 μm before and after a rapid thermal anneal at a series of temperatures. PIN photodiodes with these thick GaInNAs films in the intrinsic regions show responsivity (better than 0.5 A/W at 1.064 μm), dark current (200 nA at -2 V), and signal-to-noise ratio (greater than 105) approaching those of commercially available InGaAs/InP devices. Furthermore, it will be shown that these devices show significantly lower dark current and higher signal-to-noise ratio than similar metamorphic InGaAs/GaAs structures.

A high-intensity bowtie nano-aperture vertical-cavity surface-emitting laser for near-field optics

We demonstrated a record-high-intensity bowtie nano-aperture vertical-cavity surfaceemitting laser (VCSEL) with near-field spot size of 65 nm. The bowtie aperture VCSEL is very promising to realize near-field applications such as ultradense optical data storage.

MBE grown GaInNAs solar cells for multijunction applications

Triple-junction cells composed of III-V materials currently hold the world record for photovoltaic efficiency. In order to further increase cell efficiency in the future 4- and 5-junction cells incorporating a sub-cell with a bandgap of roughly 1.0 eV will be required. In this study 1.0 eV bandgap GaInNAs devices grown by solid source molecular beam epitaxy are investigated in terms of materials quality and device performance that show similar or better properties to the best MOVPE grown devices found in the literature. Deep-level transient spectroscopy measurements illustrate that the trap concentrations in the GaInNAs material are significantly lower than that of MOVPE grown material. The internal quantum efficiency (43%), open-circuit voltage (450 mV), short-circuit current density (25.76 mA/cm/sup 2/) and fill-factor (56.4%) of the GaInNAs devices under 1-sun power density 1064 nm radiation are similar to or surpass the properties of the best MOVPE GaInNAs devices found in the literature.

A review of progress on nano-aperture VCSEL

This paper reviews the progress on nano-aperture vertical-cavity surface-emitting lasers (VCSELs). The design, fabrication, and polarization control of nano-aperture VCSELs are reviewed. With the nano-aperture evolving from conventional circular and square aperture to unique C-shaped, H-shaped, I-shaped, and bowtie-shaped aperture, both the near-field intensity and near-field beam confinement from nano-aperture VCSELs are significantly improved. As a high-intensity compact light source with sub-100-nm spot size, nano-aperture VCSELs are promising to realize many new near-field optical systems and applications.

A high-intensity bowtie nano-aperture vertical-cavity surface-emitting laser for ultrahigh-density near-field optical data storage

We demonstrated a high-intensity bowtie-shaped nano-aperture Vertical-cavity surface-emitting laser (VCSEL). A maximum power of 188μW is achieved from a VCSEL with an 180nm bowtie aperture at a wavelength of 970nm. Simulation shows the near-field full width at half maximum intensity spot size 20nm away from the bowtie aperture is 64×66nm2. The peak near-field intensity from the bowtie-aperture VCSEL is estimated to be as high as 47mW/μm2. This intensity is high enough to realize near-field optical data storage and the small spot size corresponds to storage densities up to 150Gbits/in2.

A High-intensity Nano-aperture Vertical-Cavity Surface-Emitting Laser With Controlled Polarization

near-field optical data storage. Also, data transfer rates canbegreatly increased iftheVCSELsareapplied inparallel arrays[11. Previous workonnanoaperture VCSELsutilize conventional circular apertures whichsuffer fromlowpoweroutput through thenanoaperture whentheaperture size becomes muchsmaller thanonewavelength[23]. We propose toapply aunique C-shaped nano-aperture (C-aperture) ontoVCSELs.Fromsimulation, theC-aperture showsthree orders of magnitude higher powertransmission efficiency thanaconventional square orcircular aperture producing thesame near-field spotsize[41. We report herearecord-high near-field intensity of15.4mW/[tm2 achieved fromournanoaperture VCSELwitha70nmC-aperture. Ourtop-emitting VCSELsaredesigned tooperate around 970nmandconsist of9.5pairs ofp-type distributed Bragg reflectors (DBR),three strain-compensated InGaAs/GaAsP quantumwellsand38.5pairs ofn-DBRs.The reflectivity ofthetopmirror isenhanced witha150nmthick Aucoating. We insert ahalf-wavelength thick SiO2 filmbetween theAucoating andthetopDBR pairs toenhance thetransmission through thenano-aperture. We use wetoxidation ofAlGaAstoobtain a2.8pim-diameter oxide aperture forcurrent andmodeconfinement. Thenanoapertures areetched through theAucoating using aFocused IonBeam(FIB). Thetransmission oflight through theC-aperture ispolarization-dependent. Forthematched polarization, theCaperture produces awell-confined near-field spotwithhighintensity. However, fortheorthogonal mismatched polarization, theresulted near-field spotispoorly confined andtheintensity istwoorders ofmagnitude lower. Since VCSELsnormally havetwodegenerate orthogonal polarization states, weneedtocontrol thepolarization ofthe VCSELsinorder toapply theC-aperture ontheVCSELs.We openfour50*1500nm slits surrounding a70nmCaperture intheAu coating using FIBtocontrol thepolarization. Sincethetransmission oflight polarized perpendicular totheslit ismuchhigher thanthatoflight polarized parallel totheslit, thepolarization ofthe VCSELsiseffectively controlled tobeparallel totheslit duetolower loss inthis direction. Toidentify howmuchnetpowercomesoutoftheC-aperture, weblock thelight transmitted through theslits by depositing 150nmthick Pttofill theslits using electron-beam assisted chemical vapordeposition onaFIB/SEM dual-beam system. Pthasreflectivity of73%at1ptm, compared withreflectivity of95%forAu.Sothepolarization selectivity bytheslits ismaintained after theslits arefilled withPt.We measured thepolarization-resolved power